There is no motor in the trunk; it is a vac pump. You might just have a mechanical problem in the driver's door. Take the door card off and take a look. It is pretty simple. I had a coathanger type wire break; it pulled a plunger. Easy fix. You may just spot the problem.

Be careful and slide the door card up and then out; otherwise you will break the plastic fingers that hold it snug to the door frame.

I'll see if I have a cleaner copy.

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1983 300SD
200000miles

Does the vacuum pump have a hand crank?

There is a motor in the vacuum pump if you want to be so EXPLICIT.

If you can lock from the passenger side and not from the driver side then it is an electrical problem inside the driver door. I am not 100% sure with a 85 300SD but it should be same as the 300SDL. The vacuum pod inside the door has a 3 wires connector. When you turn the key, the common wire will make contact with either the 'lock' wire or the 'unlock' wire. If you can unlock from the driver side then the 'lock' wire is not making contact. It is either broken or bad contact. It is all part of the pod and a replacement will fix it.

Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.